Congress is slipping again, and that could mean trouble for incumbents in the upcoming elections, a new Gallup survey and analysis finds.

An April Gallup poll put Congress' approval rating at 13 percent, down from March's 15 percent and not far from the all-time November 2013 low of 9 percent.

Lawmakers haven't done much big stuff in recent weeks, and Friday are heading home for a recess that is scheduled to last until April 28.

The new numbers, said a Gallup analysis, mean "the climate could be ripe with anti-incumbent sentiment."

The approval number has never been less than 20 percent for a midterm election. But, Gallup said, "this scenario seems likely to happen in the fall unless something substantially improves Congress' image with Americans over the next few months."

Gallup also had this preview:

"Eleven states hold their primary elections next month -- with even more to come in June. The extent to which incumbency has become a liability may be most evident in races where an incumbent is fighting off a challenger within his or her own political party, and thus Obama won't be a factor. It is clear that voters, in one way or another, will have an opportunity to voice their frustrations with the job performance of the men and women they have elected to represent them this November."